ABSTRACT Automobile drivers/passengers perceive automatic transmission (AT) shift quality through the torque transferred by transmission output shaft, so that torque regulation is critical in transmission shift control and etc. However, since a physical torque sensor is expensive, current shift control in AT is usually achieved by tracking a turbine speed profile due to the lack of the transmission output torque information. A direct torque feedback has long been desired for transmission shift control enhancement. This paper addresses a “virtual” torque sensor (VTS) algorithm that can provide an accurate estimate on the torque variation in the vehicle transmission output shaft using (existing) speed sensors. We have developed the algorithm using both the transmission output speed sensor and anti-lock braking system speed sensors. Practical solutions are provided to enhance the accuracy of the algorithm. The algorithm has been successfully implemented on both FWD and RWD vehicles. Compared to the measurement from a physical torque sensor, the torque estimation from the VTS algorithm is consistent and robust under real-world driving conditions. This technology can be applicable to front wheel drive (FWD), rear wheel drive (RWD) and all wheel drive (AWD) transmissions, and provide a low-cost solution to torque- based powertrain control enhancements. INTRODUCTION Automobile transmission is the component to transfer torque from the engine to the wheels. Since the early days, there have been consistent trends towards better fuel economy, higher performance, and lighter and more compact transmissions. Control strategy has played an important role for the improved driveability and fuel economy. Precise, reliable and robust transmission control requiresmeasurement of various physical signals to determine the transmission operating conditions and enforce the necessary feedback to meet certain driveability requirements. Transmission output torque transient during gear shifting is one of the most critical driveabililty concerns. Automobile drivers/passengers perceive AT shift quality through the torque transferred by transmission output shaft. Direct information on transmission input or output torque could be useful in torque regulation by hydraulic pressure control in clutch-to-clutch shifts. However, such information is unavailable due to the high cost of a physical torque sensor and packaging issues. Current control in clutch-to-clutch shift is usually achieved by tracking a predefined turbine speed profile. Since torque transient is used as the shift control target, additional calibration and delicate adaptation algorithms are needed to compensate transmission built-to- built variations and wear and tear. Without torque measurement as feedback, undesired shifts may still occur. To simplify transmission controls and enhance the shift quality, accurate measurement of transmission input or output torque has long been desired. For years, various types of physical torque sensors have been investigated [ 1]. Sensors with sufficient accuracy and acceptable cost have been absent for successful applications. Very recently, a prototype magneto-elastic torque sensor was built and evaluated in a test vehicle [ 1]. Its relatively low cost, accuracy and reliability makes torque measurement possible in transmission within near future. Aside of this physical sensor approach, an interesting idea has been proposed to offer a low-cost way of torque estimation in transmission output shaft based on multiple speed sensors [ 2-3]. The concept is based on a well-known law of physics, i.e., the torsion of the drive shaft is proportional to the applied torque. Since the method can only determine the relative toque variation, Relative Torque Estimation on Transmission Output Shaft with Speed Sensors2011-01-0392 Published 04/12/2011 Dongxu Li, Kumaraswamy Hebbale, Chunhao Lee, Farzad Samie and Chi-Kuan Kao General Motors Company Copyright © 2011 SAE Internat